Biomarker Evaluation of Hopanoid and Steroid Distributions in some Nigerian Coals

Biomarker Evaluation of Hopanoid and Steroid Distributions in some Nigerian Coals
Biomarker Evaluation of Hopanoid and Steroid Distributions in
some Nigerian Coals
*1Uzoegbu M.U., 2Onwualu J.N.J
1,2Department of Geology, Faculty of Science, University of Port Harcourt, Port Harcourt, Nigeria.
A total of Twenty-one coal and carbonaceous shale samples were collected from four boreholes
in Mamu and Awgu Formations of Lower and Middle Benue Trough, Nigeria. The homohopane
index (C35/C31 - C35) and homohopane ratio (C35αβS/C34αβS) range from 0.02 to 0.12 and 0.15 to
0.92 indicates oxic condition during organic matter deposition from Awgu samples. The
Moretane/Hopane, Hopane/Hopane + Moretane, Ts/Ts + Tm, 22S/22S + 22RC32 homohopane ratios
range from 0.06 to 0.14; 0.88 to 0.94; 0.34 to 0.66; and 0.53 to 0.62 and 20S/20S+20R and
αββ/αββ+ααα C29 ratios range from 0.43 to 0.58 and 0.42 to 0.55 indicate samples are within the
late oil window/gas phase. Plots of 22S/22S+22R C32hopanes against C29αββ/αββ+ααα steranes
show that Awgu samples are thermally mature. The C32-C35benzohopanes were detected in
Onyeama and Okaba samples as a transformation product of C35 bacteriohopanepolyol.
C35/C30hopane ratio range from 0.01 to 0.05 and 0.01 to 0.47 indicates fluvial/deltaic and lacustrine-
fluvial/deltaic depositional environments for Onyeama and Okaba samples. The homohopane
index and homohopane ratio for the samples range from 0.02-0.13 and 0.23-0.92 indicate oxic
depositional environment for Onyeama samples and suboxic-oxic depositional environments for
Okaba samples. Moretane/Hopane, Hopane/Hopane + Moretane, Ts/Ts + Tm, 22S/22S + 22R
C32homohopane ratios in Onyeama samples range from 0.46 to 0.64; 0.61 to 0.69; 0.02 to 0.05; and
0.48 to 0.58 and Okaba ranging from 0.59-0.93; 0.54-0.64; 0.11-0.24; and 0.16-0.48 indicate that
samples are thermally immature. The sterane and diasterane distributions for all the samples
occur in the order of C29>C28>C27. The predominance of C29 sterane over C27 sterane reflects a
greater input of terrestrial relative to marine organic matter.
Keywords: Coal, Depositional environment, Hopane, Organic matter, Sterane, Thermal maturity.
INTRODUCTION
Hopanoids are considered biomarkers for bacteria and
cyanobacteria. Most hopanes molecular fossils originate
from polar constituents of prokaryotic organisms (Nytoft et
al., 2006). The most probable biological precursor of the
hopane derivatives is bacteriohopanepolyol, which are
present in the cell membranes of prokaryoticorganisms
(bacteria and blue algae) where they played the rigidifying
role by steroids in eukaryotic organisms (Ourisson et al.,
1982; Durand, 2003; Bechtel et al., 2007a, b). The C30
Hopanoids have also been found in somecryptogams;
moss, fern (Bechtel et al., 2007a, b). While hopanes with
30 or fewcarbon atoms are often interpreted as diagenetic
products of C30 hopanoids (e.g. diploptene and
diplopterol), the extended hopanes have been related to
C35 precursors, such as bacteriohopane polyols,
aminopolyols and a number of composite
hopanoids(Wang et al., 1996).
High abundance of C35hopane usually found in marine
carbonates and evaporiticsediments has been attributed to
highly reducing depositional environments (Yangming et
al., 2005).
*Corresponding Author: Uche Mmaduabuchi Uzoegbu,
Department of Geology, Faculty of Science, University of
Port Harcourt, Port Harcourt, Nigeria. Email:
uche.uzoegbu@uniport.edu.ng
Vol. 6(1), pp. 111-122, August, 2019. © www.premierpublishers.org. ISSN: 9661-0255
Research Article
International Research Journal of Chemistry and Chemical Sciences

Uzoegbu and Onwualu 112
V-shape pattern of homohopane, i.e.
C31>C32≥C33≤C34<C35 is indicative of salinelacustrine
source rock deposited under anoxic, low Eh conditions
(Peters and Moldowan, 1991; Yangming et al., 2005).
Benzohopanes, which have not beenreported in living
organisms, are thought to be secondary transformation
products ofC35 bacteriohopanepolyol derivatives (Grice et
al., 1998). Distribution and different ratios of hopanes are
used to evaluate thermal maturity of oil and source rock.
The isomerisation at C-22 can be used to assess the
maturity of geological samples (22S/22S+22R). This ratio
reflects the more thermally stable 22S isomer compared
tothe biologically derived 22R stereochemistry (Farrimond
et al., 1998; Peters et al.,2005; Killops and Killops, 2005).
The parameter is usually measured using the
C31homohopane, although the C32 homologues are
commonly employed due to co-elution of gammacerane
with C31homohopane (Farrimond et al., 1998). C27, 18a(H)-
22,29,30-Trisnorneohopane (Ts) and C27, 17a(H)-
22,29,30-Trisnorhopane (Tm) ratio are used as a maturity
indicator. Ts is knownto exhibit a greater stability than the
Tm, and with increase in maturation, Ts usuallyshows
marked increase in apparent concentration relative to the
Tm (Seifert and Moldowan, 1981). Ts/Ts+Tm ratios are not
only related to maturity, but also toorganic facies and
depositional environments. Oils derived from carbonates
usually show low Ts/Ts+Tm compared to oil generated
from shales. Bitumens of anoxic and acidic hypersaline
source rocks generally show high Ts/Ts+Tm (Seifert and
Moldowan, 1981).
Steranes are derived from sterols that are widely
distributed in plants andmicroorganisms. The relative
concentration of C27 and C29 steranes can
indicatecharacteristics source inputs and sedimentary
facies.The predominance of C27 steranes in non-marine
strata indicates a deep lake faciesand source input of
plankton (algae) while C29 sterane predominance shows a
swampshallow water environment and a terrestrial higher
plant input (Volkman and Maxwell, 1986; Peters and
Moldowan, 1993; Volkman et al., 1999; Otto et al., 2005;
Jauro et al., 2007).C28 sterane is a unique biomarker
signature of organic matter deposited in saline lacustrine
facies. Sterane/hopane ratio is often used as a measure of
the relative inputsof eukaryotic versus prokaryotic debris
(Peters and Moldowan, 1993). Low sterane/triterpane ratio
(Norgate et al., 1999) has been postulated to favour
terrestrial paralic facies rather than peat swamp facies as
organic matter source. Sterane isomerisation at C-20 has
been found useful in assessing the level of thermalmaturity
of oil and sediments. The 20S/20S+20R ratio (usually
measuredusing the C29ααα steranes) is one of the most
widely applied molecular maturityparameters in petroleum
geochemistry (Farrimond et al., 1998). It is based on
therelative enrichment of the 20S isomer compared with
the biologically inherited 20Rstereochemistry with
increasing maturity.
Sterane nuclear isomerisation ratio, (αββ/ αββ+ααα) is
widely applied owing to itsoperation beyond oil window
(Farrimond et al., 1998). In relatively immature samples,
coelution of the ααα isomer with the αββ doublet is a
common problem that isresponsible for the relatively high
αββ values at shallow depth and apparent decreasesin the
parameter with increasing depth (Farrimond et al., 1998).
In highly maturesource rocks, an eventual decrease in this
ratio occurs (Peters et al., 2005). The objective of this
research is determining the depositional environment,
organic matter source and distribution of hopanoids and
steroids in some thermally immature Nigerian coals.
STRATIGRAPHIC SETTING
The infilling of the Anambra and Afikpo started during the
Campanian to the Paleocene (Danian) under two major
eustatic cycles; the more pronounced Nkporo
transgression and the less active Nsukka transgression
with the Anambra basin showing the most complete
stratigraphic sections (Fig. 1). These cycles are also found
in the Afikpo syncline SE of the Abakaliki anticlinorium and
the Dahomey embayment, west of the Ilesha basement
spur, although both are incomplete (Murat, 1972).
The first cycle which took place during the Lower
Campanian to the Maastrichian started with the deposition
of the Nkporo whose lateral (age) equivalents are the
Enugu and Owelli (Fig. 2). This is the basal unit of the
Campano-Maastrichian transgression and comprises of
dark mudstone, gray, fissile friable shales with thin beds of
marl, sandy shale and limestone overlying an angular
unconformity (Reyment, 1965).
The regressive phase was marked with the development
of a large offlap complex, starting with the paralic
sequence of the Mamu (Lower coal measure) overlying the
Nkporo (Reyment, 1965). It is thought to be lower
Maastrichian in age with a basal part that contains thin
marine intercalations, while the coal bearing part consist of
fresh water and low salinity sandstones, shale, mudstone
and sandy shales with coal seams occurring at several
levels (Simpson, 1955).
The Mamu formation is overlain by the continental
sequence of the Ajali. This sandstone unit has received
several names such as false bedded sandstone (Tattam,
1944), basal sandstone (Simpson, 1955) etc. Its present
name was given by Reyment (1965) after establishing its
type locality at the Ajali. Virtually all exposures of the
formation are characterized by a lateritic profile at the top.
It was deposited during the regressive phase of the
Campano-Maastrichian transgression and the age is
Maastricthian.
The Ajali sandstone is overlain conformably by the Nsukka
Formation (Upper coal measures), and it consists of
alternating succession of gray sandy shales, sandstones,
plant bearing beds and thin beds of coal (Reyment, 1965).
Thin bands of marine limestone heralded the return of
marine sedimentation at the top of the formation. These

Int. Res. J. Chem. Chem. Sci. 113
dark shales and the intensely bioturbated sandstones are
well exposed at Ihube, along the Enugu – Port Harcourt
expressway. The age range of the formation is late
Maastrichian to Danian based on the fossil record. This
formation bears the K/T boundary which is described by
Reyment (1965) as a period of transition in Nigeria. Mbuk
et al. (1985) identified this boundary in the Nsukka
Formation in OzuAbam area of Abia State.
Fig. 1: Generalized geological map of Nigeria (boxed areas of inset) showing the geological map of the Anambra Basin.
Numbers indicate Cretaceous and Tertiary formations shown as follows: 1.Asu River Group; 2. Odikpani Formation;
3.Eze-Aku Shale; 4.Awgu Shale; 5. Enugu/Nkporo Shale; 6.Mamu Formation; 7.Ajali Sandstone; 8. Nsukka Formation; 9.
Imo Shale; 10.Ameki Formation and 11.Ogwashi-Asaba Formation (after Akande et al., 2007).
MATERIALS AND METHODS
A total of nine samples comprising of six coals, two
carbonaceous shales and one coaly shale were collected
from 2 boreholes (BH94 and BH120) from Awgu Formation
(BH). The coal seams and interbedded shale in BH94 and
BH120 were sampled between 218-431 m and 131- 289
m depths respectively. In Mamu Formation, twelve
samples consisting of nine coals and three carbonaceous
shales were collected from Okaba (OBA) and Onyeama
(AMA) with co-ordinates of 07o 28ˈN, 07o 43ˈE and 06o 28ˈ
N, 07o 26ˈE).
In the laboratory, the samples were reshaped using a
rotating steel cutter to eliminate surface that could be
affected by alteration. Chips were cut from the samples
and dried in an oven at 105oC for 24 hours. The dried
sample was pulverized in a rotating disc mill to yield about
50 g of sample for analytical geochemistry. The samples
were subjected to flame ionization detection (FID) for
hydrocarbons thermal conductivity detection (TCD) for
CO2. One milligram of bulk powder sample was added to
200 mg of KBr and the mixture homogenized using a
pestle in an agate mortar. Pressing the mixture using a
load of 10 t yielded a pellet for Fourier Transform Infrared
(FT-IR) Spectroscopy using a Nicolet Bench 505P
Spectrometer, with sample absorbance monitored using
256 scans with resolution of 4 cm-1 from a wave-number of
4000 – 400 cm-1. About 10 g of the sample was subjected
to sohxlett extraction using a solvent mixture of acetone,
chloroform and methanol (47: 30: 23 v/v) at 60oC for 24
hours to extract the soluble organic matter. The extract
was concentrated by evaporation to dryness using a
rotating vapour evaporator at 250 mb. The extract was

Fig. 2: The Stratigraphy of the Anambra Basin Southeastern Nigeria (After,Ladipo, 1988 and Akande et al., 1992; Modified
in Uzoegbu et al., 2013b).
transferred to an 8 ml vial using the same solvent mixture
and allowed to evaporate to dryness in a vented hood. The
dried extract was fractionated by silica gel column
chromatography with a column prepared using 2 g of baker
silica gel calcined at 200oC for 24 hours to yield six
fractions ranging from saturate to polar.
The saturate fraction was subjected to urea adduction to
separate isoprenoids from n-alkanes and subjected to gas
chromatography-mass spectrometry (GC-MS) using a CE
5980 GC coupled to an HP Finnigan 8222 MS held at 80oC
for three minutes and raised to 310oC at 3oC min-1 and held
isothermally for 10 minutes in order to assess some
molecular parameters used in source rock
characterization.
RESULT AND DISCUSSION
The m/z 191 mass chromatograms showing the
distribution of pentacyclic triterpanes in the samples are
shown in Figs. 3, 4 and 5. C29 and C30αβ-hopane occur in
appreciable amount in all the Awgu coaly shale samples
(Fig. 3), indicating significant contribution of prokaryotic
organisms(i.e. bacteria, cyanobacteria and blue algae) to
the source organic matter (Adedosu, 2009).The
sterane/hopane ratio is often used as a measure of relative
inputs of eukaryoticversus prokaryotic debris (Peters and
Moldowan, 1993). The sterane/hopane ratio values range
from 0.04-0.51(Table 1).
The ratio values (<0.6) according to (Tissot and Welte,
1984; Peters and Moldowan, 1993; Sachsenhofer et al.,
2000; Norgate et al., 1999) indicative of theincorporation
of high level of bacterial inputs commonly associated with
terrigenousorganic matter in coals (non-marine organic
matter).The appreciable quantity of homohopanes (C31-
C35) in all the samples, suggest that bacteriohopanetetrol
and other polyfunctional C35 hopanoids;
bacteriohopanepolyols, aminopolyols etc. (Wang et al.,
1996; Adedosu, 2009), common in prokaryotic micro-
organisms (Ourrisson et al., 1979; Rohmer, 1987) were
significant contributors to the biomass.
The occurrence of 18α(H)-28-noroleanane, 18α(H)- and
18β(H)-oleanane in Awgu coaly shale samples is notable.
Oleananes are regarded as reliable marker
forangiosperm; being significant constituents of wood,
roots and bark in Cretaceous oryounger effective source
rocks in deltaic petroleum system (Moldowan et al.,
1994;Nytoftet al., 2002; Peters et al., 2005; Ozcelik and
Altunsoy, 2005; Otto et al., 2005;Bechtel et al., 2007b).
AGE
SEDIMENTARY
SEQUENCE
LITHOLOGY DESCRIPTION DEPOSITIONAL
ENVIRONMENT
REMARKS
ANKPA
SUB-
BASIN
ONITSHA
SUB-
BASIN
MIOCENE
OLIGOCENE
OGWASHI-
ASABA FM.
Lignites, peats,
Intercalations of
Sandstones &
shales
Estuarine
(off shore bars;
Intertidal flats)
Liginites
EOCENE AMEKE NANKA
FM. SAND
Clays,shales,
Sandstones
& beds of grits
Unconformity
Subtidal, intertidal
flats, shallow marine
PALEOCENE
IMO SHALE Clays, shales
& siltstones
Marine
MAASTRICHTIAN
Clays, shales, thin
sandstones & coal
seams
Coarse sandstones,
Lenticular shales,
beds of grits &
Pebbls.
Clays, shales,
carbonaceous
shale, sandy shale
& coal seams
NSUKKA FM.
AJALI SST.
MAMU FM.
? Estuarine
Subtidal, shallow
marine
Estuarine/ off-shore
bars/ tidal flats/
chernier ridges
CAMPANIAN
ENUGU/
NKPORO SHALE Clays & shales Marine
CONIACIAN-
SANTONIAN
AWGU SHALE
TURONIAN EZEAKU SHALE
Clays &
shales Marine
ODUKPANI FM.
CENOMANIAN
ALBIAN
L. PALEOZOIC
ASU RIVER GP.
B A S E M E N T C O M P L E X
Sub-
bituminous
Sub-
bituminous
3rd Marine
cycle
Unconformity
2nd Marine
cycle
Unconformity
1st Marine
cycle
Unconformity
NODEPOSITION
(? MINOR
REGRESSION
REGRESSION
(Continued
Transgression
Due to geoidal
Sea level rise)
TRANSGRESSION
(Geoidal sea level
Rise plus crustal
Movement)
Coal
Rank
~
~ ~
~
~
~ ~
~ ~
~ ~
~
~
~
~
~
~
~ ~
~
~ ~
~
~ ~
~ ~
~ ~
~ ~
~
~
~ ~
~~
~
~
~
~
~
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~ ~ ~
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
.
. .
. ..
... .
... .

The C35/C30hopane ratio values range from 0.03 to 0.26,
which reflects organicmatter deposited in lacustrine-
fluvial/deltaic environments (Peters et al., 2005). The
homohopane index (C35/C31 - C35) and homohopane ratio
(C35αβS/C34αβS) range from 0.02 to 0.12 and 0.15 to 0.92
respectively (Table 1). The low homohopane index of the
samples indicates oxic condition during organic matter
deposition (Peters and Moldowan, 1991; Hanson et al.,
2001; Killops and Killops, 2005; Peterset al., 2005;
Yangming et al., 2005; Adedosu, 2009).
Hopanes with αβ epimers are more prominent in all the
samples (Table 2) while no ββ-epimeris detected.
Homohopanes ranging from C31-C35 showed notable
predominance of the22S over the 22R epimer (Fig. 3).
These observations reflect high maturity statusof the
samples (Miranda et al., 1999; Peters et al., 2005; Tuo et
al., 2007; Adedosu, 2009).The Moretane/Hopane,
Hopane/Hopane + Moretane, Ts/Ts + Tm, 22S/22S +
22RC32homohopane ratios range from 0.06 to 0.14; 0.88
to 0.94; 0.34 to 0.66; and 0.53 to0.62 respectively. These
values indicate samples are within the late oil window/gas
phase (Seifert and Moldowan, 1986; Mackenzie, 1984;
Seifert and Moldowan, 1986; Peters and Moldowan, 1993;
Kagya, 1996; Tuo et al., 1999; Peters et al., 2005;
Adedosu, 2009).
Fig. 3: m/z 191 Mass chromatogram showing the Fig. 4: m/z 191 Mass chromatogram showing the distribution of
distribution of hopanes in Awgu samples. hopanes and benzohopanes in Mamu sample (Okaba).
Fig. 5: m/z 191 mass chromatogram showing the distribution of hopanes and benzohopanes in Mamu samples
(Onyeama).

Table 1: Source and depositional environment parameters computed from the hopane and sterane distributions in the
coals.
Sterane/Hopane=C27+C28+C29steranes/[(C29+C30)αβhopane + (C31+C32+C33)αβ(R+S) homohopane]
C35/C30 = C35αβ(R+S) homohopane/ C30αβ hopane + C30βα moretane
Homohopane ratio,C35/C34αβS = C35αβS/C34αβS homohopane
Homohopane index = C35/ C31+C32+C33+C34+C35) αβ(R+S) homohopane
Table 2: Maturity parameters computed from the hopane and sterane distributions in the coals.
Mor/Hop = Moretane/Hopane (C30)
Hop/Hop + Mor = Hopane/Hopane + Moretane (C30)
C32HH = C32homohopane

The C27 to C35hopanes are detected in all the Mamu
samples but C28 was notdetected (Fig. 4 and 5). The most
prominent hopane in Onyeama samples areC29αβ-
norhopane and C30αβ-hopane while C29αβ norhopane is
predominant in Okaba samples (Fig 4 and 5). In the Okaba
samples, abundance of C29αβ-hopane in allthe samples
reflects major contribution from terrestrial organic matter;
however,contribution from prokaryotic organisms is not
excluded while abundant C30αβ-hopane with notable
presence of C29αβ in Onyeama samples reflects significant
contribution from prokaryotic organisms as well as vitrinitic
(terrestrial) organic matter (Adedosu, 2009). The unusual
high abundance of 22R compared to 22S in the C31-17α
(H),21β(H) homohopane is evident in all Okaba samples.
This is likely due to co-elution of gammacerane (Peter and
Moldowan, 1993; Kagya, 1996; Farrimond et al., 1998;
Peters et al., 2005).
Benzohopanes with different distributions were found in
Onyeama and Okaba coal samples (Fig. 4 and 5). There
is no previous record of presence of benzohopanes in
Nigerian coal and coaly organic matter. The C32-
C35benzohopaneswere detected in Onyeama samples
while C32-C33benzohopanes were detected in Okaba
samples (Adedosu, 2009). Benzohopanes are thought to
be secondary transformation products ofC35
bacteriohopanepolyol derivatives (Grice et al., 1998;
Peters et al., 2005; Killops and Killops, 2005; Bechtel et
al., 2007a).
Fig. 6: Mass frangmentogram and spectra of Olean-18-ene in Okaba coal samples.
Fig. 7: Mass frangmentogram and spectra of Olean-13(18)-ene in Okaba coal samples.

Fig. 8: Mass frangmentogram and spectra of Olean-12-
ene in Okaba coal samples.
Three isomers of oleanenes; olean-18-ene, olean-13 (18)-
ene and olean-12-ene were identified in Okaba samples
(Fig. 6, 7 and 8). Similar to the benzohopanes, this is the
first time oleanene isomers are being identified in Nigerian
coal and coaly organic matter (Adedosu, 2009). These
three oleanene isomers are products of late diagenesis
from taraxerol and β-amyrin, which are biomarkers for
angiosperm (Ten Haven and Rullkötter, 1988; Ekweozor
and Telnǽs, 1990; Rullkötter et al., 1994; Curiale, 1995).
They have also been found useful as indicators of thermal
immaturity (Eneogwe et al.,2002).
In Onyeama sample, C35/C30hopane ratio range from 0.01
to 0.05 while Okaba samples have values ranging from
0.01 to 0.47. These values indicate fluvial/deltaicand
lacustrine-fluvial/deltaic depositional environments for
Onyeama and Okaba samples respectively. The
homohopane index and homohopane ratio for the samples
ranges from 0.02-0.13 and 0.23-0.92 respectively (Table
1). These values indicate oxic depositional environment for
Onyeama samples and suboxic-oxic depositional
environments for Okaba samples (Peters and Moldowan,
1991; Killops and Killops,2005; Peters et al., 2005;
Yangming et al., 2005). There is presence of
gammacerane in Okaba samples (Fig. 4 and 5), which
indicate water column stratificationduring organic matter
source deposition (Sinninghe-Damsté et al., 1995;
Yangming et al., 2005; Adedosu, 2009).
In Table 2 Moretane/Hopane, Hopane/Hopane +
Moretane, Ts/Ts + Tm, 22S/22S + 22RC32homohopane
ratios in Onyeama samples range from 0.46 to 0.64; 0.61
to 0.69;0.02 to 0.05; and 0.48 to 0.58 respectively. These
values suggest low maturity status (Rullkötter et al., 1985;
Kagya, 1996; Peters et al., 2005). The Okaba samples
have Moretane/Hopane, Hopane/Hopane + Moretane,
Ts/Ts + Tm, 22S/22S + 22R C32homohopane ratios
ranging from 0.59-0.93; 0.54-0.64; 0.11-0.24; and 0.16-
0.48respectively. These values also indicate that
Onyeama samples are thermally immature (Rullköteret al.,
1985; Kagya, 1996; Peters et al., 2005).
The m/z 217 mass chromatograms showing the
distribution of steranes and diasteranes in all the samples
are shown in Figs. 9, 10 and 11. The occurrence of C27 to
C29 steranes and diasteranes were detected in Awgu coaly
samples (Fig. 9). The sterane and diasterane distributions
for all the samplesoccur in the order of C29>C28>C27 (Table
1). The predominance of C29 sterane overC27 sterane
reflects a greater input of terrestrial relative to marine
organic matter(Huang and Meinschein, 1979; Volkman
1988; Kagya, 1996; Sari and Bahtiyar, 1999;Otto et al.,
2005; Peters et al., 2005). The ternary plots of sterane
distribution in Awgu samples (Fig. 12) indicate organic
matter derived from terrestrial materialsdeposited in
lacustrine – fluvial/deltaic settings (Huang and Meinschein,
1979; Killops and Killops, 1993, 2005; Peters et al., 2005).
The diasterane ternary plots (Fig. 13) also show that Awgu
samples are from terrestrial organic matter. This
observation is supported by C27/C29 ratios (Table 1), which
range from 0.28 to 0.56(Peters et al., 2005). The
dominance of dinosterol over C30 steranes in these
samples reflects typical fresh water lacustrine source
rocks (Köhler and Clausing, 2000; Peters et al., 2005).
The 20S/20S+20R and αββ/αββ+ααα C29 ratios range
from 0.43 to 0.58 and 0.42to 0.55 respectively. These
values show that the samples are within the oil
generativewindow (Peters et al., 2005; Adedosu, 2009).
Plots of 22S/22S+22R C32hopanes against
C29αββ/αββ+ααα steranes show that Awgu samples are
thermally mature (Fig. 14).
Fig. 9: m/z 217 mass chromatograms showing the
distribution of steranes and diasteranes in Awgu samples.

distribution of steranes and diasteranes in Mamu samples
(Okaba).
distribution of steranes and diasteranes in Mamu samples
(Onyeama).
Fig. 12: Ternary plots of C27, C28 and C29 steranes
distributions in Nigeriancoal (After Huang and Meinschein,
1979).
Fig. 13: Ternary plots of C27, C28 and C29diasteranes
distributions in Nigerian coal (After Huang and Meinschein,
1979).
Fig. 14: Plots of 22S/22S+22R C32hopanes against
C29αββ/αββ+ααα steranes(After Inaba et al., 2001).
C29Diasteranes and steranes are the most abundant
steranes in all the samplesexcept few samples from
Okaba where C28 predominates. The sterane and
diasterane distributions in Okaba samples are increasing
in the order of C29>C28>C27.The predominance of C29 over
C27 sterane reflects a greater input of terrestrial relativeto
marine organic matter (Huang and Meinschein, 1979;
Volkman, 1988; Kagya, 1996;Sari and Bahtiyar, 1999; Otto
et al., 2005; Peters et al., 2005; Adedosu, 2009). The
appreciablequantity of C27 and C28 in these samples also
reflect contributions from phytoplankton; algae, diatoms,
dinoflagellates (Volkman, 1986; Volkman et al., 1998; Sari
and Bahtiyar, 1999; Peters et al., 2005). The ternary plot
of C27, C28 and C29 sterane of Mamu samples (Fig. 12)
reflects major terrestrial input in Onyeama samples while
Okaba samples consist of both terrestrial and marine
organic matter (Huang and Meinschein, 1979; Killops and
Killops, 1993, 2005; Peters et al., 2005).The diasterane
ternary plot (Fig. 13) shows that most of the Onyeama
samples are derived from terrestrial organic matter with

few samples having mixed inputs (i.e. terrestrial and
marine). Samples from Okaba are majorly derived from
mixedorigin. There is little variation in sterane and
diasterane distribution in Onyeama samples while
significant variations are noticed in Okaba samples. This
observationpossibly reflects same depositional
environments for Onyeama samples(fluvial/deltaic) and
lacustrine-fluvial/deltaic depositional environments for
Okaba samples (Adedosu, 2009). This observation can be
supported by the ratio of C27/C29 (Table 1) for thesamples.
The values range from 0.2 to 0.7 and 0.18 to 0.43 in Okaba
and Onyeama samples respectively. The dominance of
dinosterol over C30 steranes in Okaba samples reflects
typical fresh water lacustrine source rocks (Köhler and
Clausing,2000; Peters et al., 2005; Adedosu, 2009).
The 20S/20S+20R and αββ/αββ+ααα C29 ratios range
from 0.04 to 0.19 and 0.16to 0.25 respectively in Onyeama
samples while the values range from 0.1 to 0.39 and0.21
to 0.56 respectively in Okaba samples. The generally low
values recorded according to Adedosu (2009) indicate that
the samples are thermally immature (Table 2). The plot of
22S/22S+22R C32hopanes against C29αββ/αββ+ααα
steranes also confirm the thermal immaturity status of
Mamu samples (Fig. 14).
CONCLUSION
Coal and coaly organic matter samples were collected
from coal bearing measures of Lower and Middle Benue
Trough, Nigeria. A total of nine samples comprising of six
coals, two carbonaceous shales and one coaly shale
sample were collected from 2 boreholes (BH94 and
BH120) from Awgu Formation (BH). In Mamu Formation,
twelve samples consisting of nine coals and three
carbonaceous shales were collected from Okaba and
Onyeama coal seams. The C32-C35benzohopanes were
identified in Onyeama and Okaba samples. The
homohopane index (C35/C31 - C35) and homohopane ratio
(C35αβS/C34αβS) indicates oxic - suboxic conditions during
organic matter deposition from Awgu and Mamu samples.
The Moretane/Hopane, Hopane/Hopane + Moretane,
Ts/Ts + Tm, 22S/22S + 22RC32homohopane ratios and
20S/20S+20R and αββ/αββ+ααα C29 ratios indicate
samples are within the early to late oil window/gas phase.
Plots of 22S/22S+22R C32hopanes against
C29αββ/αββ+ααα steranes show that Awgu and Mamu
samples are thermally immature to mature stage.
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Accepted 26 July 2019
Citation: Uzoegbu M.U., Onwualu J.N.J (2019).
Biomarker Evaluation of Hopanoid and Steroid
Distributions in some Nigerian Coals. International
Research Journal of Chemistry and Chemical Sciences
6(1): 111-122.
Copyright: © 2019. Uzoegbu and Onwualu. This is an
open-access article distributed under the terms of the
Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any
medium, provided the original author and source are cited.

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